NASA's Earth Observing 1 (EO-1) spacecraft has been operating in orbit for 8 years today. This technology demonstrator, a single-string spacecraft with essentially no redundancy, has operated, without rebooting(!) since being powered up before launch. EO-1's primary mission was completed in 6 months, and the satellite was originally designed for a 1 year life.
EO-1 now provides replacement science for a failed instrument on Landsat-7, and has archived more than 40,000 images. Enhanced algorithms have been uploaded into the WARP processor that now can detect fire and flooding conditions, and the operations team can semi-automatically task other satellites to look at those same regions in later orbits. Information is also coordinated with unmanned aerial vehicles, and mashed together for display with Google Earth.

I was the software integration lead on EO-1, and the team that built this little bird was terrific. This was my first satellite job and was the first launch I ever attended. The flight software was delivered under budget and the final build was delivered a week ahead of schedule.

Thanks for looking. This is one of NASA's little-known achievements that I think needs a wider audience.

I've asked everyone I can get in contact with on the operations team and everybody has told me it's never rebooted. I'm pretty proud of that fact, and my group gets a lot of marketing mileage out of it

It's running VxWorks on a Mongoose V processor which is a MIPS R-3000 derivative, running at 12Mhz. 256MB DRAM, 4MB EEPROM, and the code fits in about 1.6MB or so (there's 2 copies in EEPROM for backup).
In addition to the main code, there's an AI engine which does orbital prediction and calculates Delta-V burns to keep the satellite formation flying with Landsat-7. They broke formation about - what - maybe 2 years ago to save fuel. Landsat-7 is the size of a schoolbus and slows down much faster due to atmospheric drag, so little EO-1 had to put the brakes on frequently to keep in formation (we followed L7's ground track by I think 15 minutes). So I'm not sure if the AI engine is still running the show, but probably (just not in formation with L7).